Nerve growth factor (NGF) is a protein required for the development, maintenance, and repair of the nervous system. There are two NGF receptors, gp75 and the tyrosine kinase TrkA. Both of these receptors can signal separately and they synergize with each other to activate multiple signal transduction pathways. The investigators hypothesize that NGF-induced receptor dimerization and clustering are the initiating These studies may provide a physical basis for NGF receptor signaling and, thereby, aid the development of new approaches for enhancing neuronal survival following trauma or during neurodegenerative disease.